The invention relates to a device for forming an oxide film on a semiconductor under high pressures.
Oxide film forming devices of the type referred to have been commonly employed to manufacture a variety of planar type integrated circuits including a semiconductor substrate composed of silicon. In this case, it has been required to form an oxide film consisting of silicon dioxide and having a thickness of from about 1 to 2 microns while remaining substantially uncontaminated. In order to form such a thick film of silicon dioxide, it has been necessary to heat the silicon substrate in an oxidizing atmosphere at about 1,000.degree. C. for about ten hours. Such an oxidizing atmosphere can comprise, for example, saturated steam at 100.degree. C. under one atm. The heating for such a long time has been undesirable because it increases the lattice defects in the silicon substrate and/or it brings about the re-diffusion of a diffusion layer formed on the silicon substrate.
In order to avoid these disadvantages, there have already been proposed devices comprising a pressure envelope for accommodating silicon substrates therein, heating means disposed in the envelope to heat the silicon substrates to about 1,000.degree. C. and boosting means for raising the particular oxidizing atmosphere to about 10 atm. By maintaining the oxidizing atmosphere at that elevated temperature under such a high pressure, the silicon dioxide film has been formed on silicon substrates at a greatly accelerated growth.
In the conventional devices as above described, the heating means has included a heat generating element disposed in the same envelope as the silicon substrates. Therefore it has been possible for that portion of the oxidizing atmosphere contacted by the heat generating element to contact the silicon substrates.
Also because the pressurized steam involved is generated by an associated boiler, contaminating materials originating from the boiler have been mixed with the steam. Therefore the silicon substrates and silicon dioxide films formed thereon become contaminated. As a result, the proposed devices have not been always satisfactory.
Accordingly it is an object of the present invention to provide a new and improved oxide film-forming device for effecting the oxidization with steam under a high pressure.
It is another object of the present invention to provide a new and improved device for forming a clean, thick oxide film in short time interval.
It is still another object of the present invention to provide an oxide film-forming device of the type as above described in the preceding paragraph which is relatively simply constructed with cheap materials.